Install the Blackfire extension from the Mozilla Add-On website:
The Firefox extension is automatically updated by the Firefox Scheduler.
The browser extension injects a toolbar in the profiled webpage and uses an
<iframe> to communicate with the probe.
In case the web page declares a Content Security Policy regarding frames usage, the communication may be broken and you would be informed in the toolbar.
In this case, you can declare Blackfire domain as trusted by adding the
blackfire.io domain in your application’s headers:
Content-Security-Policy: frame-src 'self' blackfire.io